Lots of support, only at the top. Why did Dave dive alone so deep???

Please I mean no disrespect here.

Can someone please explain:

1) Was the plan poorly conceived? And why have so many non-qualified divers who could not go deeper planned to offer support only at the top of the dive and one diver to recover the body?

2) Was Don supposed to accompany Dave? What equipment broke to stop him from joining Dave.

3) Hindsight being 20/20, but would this have turned out differently if 3 qualified divers went down to get the body, not some complicated support plan, where divers were just not qualified or capable to assist. Was the plan not obviously foolhardy to begin with (I have no diving knowledge).

Bizarre oversight to a tragic story. RIP Dave